The present invention relates to a method of transferring information between two terminal devices using infrared wavelength range. The invention is in particular related to two-way data transfer using the same infrared wavelength range, and terminal devices between which the data transfer is carried out.
In the modern information society numerous portable terminal devices are used, such as advanced computers, mobile stations and pocket computers. It is very often necessary to transfer information from these terminal devices to some other device, such as a normal computer, and correspondingly to receive data from this other device. This data transfer is typically realized either using a cable specially manufactured for this purpose, but nowadays more and more extensively using an infrared connection. An infrared connection is a fast, and on short distances reliable, way to transfer data.
Previously an infrared connection between two devices was realized using different manufacturers"" own standards (proprietary standards). This naturally reduced the compatibility of terminal devices of different brands and infrared connections becoming more common. In applications in which compatibility was not required, such as remote control of domestic appliances, using infrared connections quickly became common. It would be to the advantage of different manufacturers, but above all to the advantage of end users, if there were one general standard for data transfer realized using infrared connection. One of the solutions aiming at this target is the the IrDA (Infrared Data Association) -standard.
The IrDA -standard, known to a person skilled in the art, is a data transfer protocol for one-way serial data. Utilizing it, it is possible to transfer data between two terminal devices alternately using infrared wavelength range from 850 to 900 nm. In many cases a simultaneous, two-way (full duplex) data transfer would be a great advantage. The IrDa -standard does not offer this possibility; nor does any other prior art data transfer system operating in the infrared wavelength range.
Now an infrared link has been invented, in which it is possible to transfer data between two terminal devices simultaneously in both directions (full duplex). An infrared link according to the invention is preferably realized using linearly polarized infrared light, but it is also possible to use other wavelength ranges. A data transfer channel to be formed using an infrared connection is divided into two separate channels using polarization. The polarization of light is achieved using e.g. polarizers, beam-splitters or birefracting crystals. In this way, when data is transferred between two terminal devices, data transfer in one direction is realized e.g. using vertically polarized infrared light, and correspondingly in the other direction using horizontally polarized infrared light. The data transfer is preferably realized using a direct light beam, but it is also possible to realize it using an optical fiber cable with suitable optical properties.
An infrared link according to the invention facilitates interrupting of the otherwise uninterrupted data transfer connection at the request of the receiving terminal device. In such a case the receiving terminal device can e.g. inform of the filling up of the buffer memory of the receiver in order to interrupt the data transmission. Correspondingly, data transfer errors can easily and quickly be corrected straight after they are detected, because the receiving terminal device can request a re-transmission immediately after having detected the errors. In addition to the above, two-way data transfer preferably makes data transfer faster on such occasions in which data is exchanged between two terminal devices. The bigger the volume of the data transfer required, the bigger the benefit achieved with the invention.
In an infrared link according to the invention a data transfer channel operating at infrared wavelength range is divided into two parts utilizing polarization. In one embodiment of the invention it is possible to use the created two data transfer channels for data transfer to a certain two terminal device. In this way, when data is transferred from transmitter A to receiver B or C, transmitter A can select the receiving terminal device B or C using the polarization of the infrared light it emits. This is realized e.g. by providing receiver B with a horizontal polarizer and receiver C with a vertical polarizer, and transmitter A with transmitting means which are capable of transmitting both horizontally and vertically polarized infrared light as chosen.
In another embodiment of the invention dividing an infrared data transfer channel operating at infrared wavelength range into two channels, achieved by polarization, preferably facilitates also the doubling of the data transfer capacity of the data transfer channel. This has been realized in such a way that a transmitter is provided with two separate transmitter units, of which one transmits data using horizontally polarized infrared light and the other using vertically polarized infrared light. In a receiver the informations are separated from each other using horizontal and vertical polarizers or a beam splitter. In this way it is possible, using an IrDA-connection capable of 4 Mbps data transfer rate, to transfer data at a total data transfer rate of 8 Mbps. Because the data transfer channels separated from each other using polarization are independent of each other, the system according to the invention also facilitates the realization of two 4 Mbps data transfer channels simultaneously.
The features characteristic of the infrared link according to the invention are presented in the characterizing parts of the claims.